Device for light based skin treatment

ABSTRACT

A device ( 10 ) for light based skin treatment is provided. The device ( 10 ) comprises a light source ( 18 ) for providing an incident light beam ( 21 ) for treating a skin ( 30 ), optical elements for focusing the incident light beam ( 21 ) in a focal point ( 22 ) inside the skin ( 30 ), and a skin interface element ( 11 ) for, during use of the device ( 10 ), providing optical coupling of the incident light beam ( 21 ) from the device ( 10 ) into the skin ( 30 ). The skin interface element ( 11 ) comprises a transparent exit window ( 12 ) for allowing the incident light beam ( 21 ) to leave the device ( 10 ), on top of the exit window ( 12 ), a transparent mixture ( 13 ) of a polar substance and an apolar substance, and on top of the transparent mixture ( 13 ), a transparent foil ( 14 ), the transparent foil ( 14 ) being more hydrophobic than the exit window ( 12 ).

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application claims the benefit or priority of and describesrelationships between the following applications: wherein thisapplication is a divisional of U.S. patent application Ser. No.14/381,329, filed Aug. 27, 2014, which is the National Stage ofInternational Application No. PCT/IB2013/051560, filed Feb. 27, 2013,all of which are incorporated herein in whole by reference.

FIELD OF THE INVENTION

This invention relates to a device for light based skin treatment, thedevice comprising a light source for providing an incident light beamfor treating a skin, optical elements for focusing the incident lightbeam in a focal point inside the skin, and a skin interface element for,during use of the device, providing optical coupling of the incidentlight beam from the device into the skin, the skin interface elementcomprising a transparent exit window for allowing the incident lightbeam to leave the device.

This invention further relates to a system for light based skintreatment, to a coupling foil and a method for providing opticalcoupling of an incident light beam from a device for light based skintreatment into a skin.

BACKGROUND OF THE INVENTION

Such a skin treatment device is, e.g., known from the publishedinternational patent application WO 2008/001284 A2. Said applicationdiscloses a skin treatment device with a laser source and focusingoptics. The device comprises a housing with an exit window through whicha laser beam is emitted. The exit window may be made of a transparentmaterial or may simply be an aperture in the housing. The device createsa focal spot in a dermis layer of the skin to be treated. The power ofthe laser beam and the dimensions of the focal spot are selected suchthat laser induced optical breakdown (LIOB) is induced in the focal spotin the skin in order to stimulate re-growth of skin tissue and to reducewrinkles.

The focal spot is created at a fixed treatment depth, somewhere between0.2 and 2.0 mm. This depth is selected based on the typical compositionof human skin. In some cases, however, the optimal treatment depth maybe different. The optimal treatment depth depends on, e.g., thethickness of the stratum corneum and the epidermis. To prevent a lenseffect by the skin and by the curvature of the wrinkle, anindex-matching material may be applied to the skin in order to fill thewrinkle between the epidermis and the exit window. The index-matchingmaterial should have an index of refraction approximately between theindex of refraction of the exit window and that of the epidermis,preferably approximately equal to the refractive index of the epidermis.In the ideal case, the exit window and the index-matching material havethe same index of refraction as the epidermis, i.e. roughly 1.4.

However, the mere addition of an index-matching material in order toprevent a mismatch in the refractive index is not sufficient forobtaining the desired control over the light intensity in the focal spotand over the exact position of the focal spot in the skin. The skinsurface (stratum corneum) shows microscopic fluctuations in roughnessdue to vertically stacked corneocytes. The coupling of light through theoptically rough stratum corneum, which resembles an array of microlenses, is difficult and results in loosely focused light beams. Thiscauses a decrease of the ratio of the photon density in the focal spotto the background and a less efficient LIOB creation in the focus.

OBJECT OF THE INVENTION

It is an object of the invention to improve the coupling of the lightinto the skin and the efficiency of the LIOB creation in the dermis.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, this object is achieved byproviding a device for light based skin treatment, the device comprisinga light source, optical elements and a skin interface element. The lightsource provides an incident light beam for treating a skin. The opticalelements are provided for focusing the incident light beam in a focalpoint inside the skin. The skin interface element, during use of thedevice, provides optical coupling of the incident light beam from thedevice into the skin. The skin interface element comprises a transparentexit window for allowing the incident light beam to leave the device. Ontop of the exit window, a transparent mixture of a polar substance andan apolar substance is provided. A transparent foil is provided on topof the transparent mixture. The transparent foil is more hydrophobicthan the transparent exit window.

With such a skin interface element comprising different layers withdifferent physical, optical and chemical properties, the coupling of thelight into the skin is significantly improved. Like in the already knownoptical skin treatment device, the surface of the exit window flattensthe skin. This mechanical flattening is, however, not sufficient forobtaining the desired efficient LIOB creation. From, e.g., theinternational patent application WO 2010/031777 it is known to use a gelfor reducing a mismatch between the refractive indexes of the skin andthe exit window. Such a gel, however, does also not overcome the opticalcoupling problems associated with the rough surface of the stratumcorneum.

The inventors have obtained better results using massage oils or othertypes of organic oils. The strong capillary effect of the oil improvesthe optical coupling between the interface element and the top layers ofthe skin. It is to be noted that this capillary effect can also beprovided by other fluids having a suitable viscosity of about 20 toabout 80 mPa·s, preferably about 20 mPa·s. The capillary effect of thefluid overcomes the microstructure variations and enables the efficientoptical coupling. The capillary effect is proportional to the surfacetension of the fluid, radius of capillary etc. . . . . Furthermore, theaction will be faster for low viscous fluids. Highly viscous fluids canalso provide the desired capillary action, however at relatively slowspeeds. This result in slight modification of the radius of capillary asthe drop of fluid is pulled along the surface of skin, thereby enhancingthe effect.

Also the contact angle that the drop of viscous fluid makes as it comesin contact with the skin affects the speed of the capillary action.Preferred contact angles between the fluid and the skin are in the range0-45°, and smaller contact angles are preferred over larger angles.

According to the invention, this capillary effect is significantlyenhanced by adding the transparent and relatively hydrophobic foil andthe transparent mixture of a polar and an apolar substance between theskin and the transparent exit window. The transparent mixture providesfor a smooth transition between the more hydrophilic transparent exitwindow, which is usually made of glass or a plastics material, and thefoil, which results in a flat foil surface. The surface of the foil andthe skin allow the applied oil to be effectively smeared throughout themicrostructure variations of the stratum corneum, resulting in uniformoptical coupling.

The transparent mixture is provided on top of the exit window and thefoil is applied on top of the mixture. Regardless of the actualorientation of the device, ‘on top’ means that it is the next layer seenfrom the direction of the incident light beam coming from the lightsource.

For optimal optical coupling between the device and the skin, thetransparent mixture should have a refractive index that lies between therefractive indexes of the foil and the transparent exit window.

According to a further aspect of the invention, a coupling foil isprovided for optically coupling an incident light beam from atransparent exit window of a skin interface element of a device forlight based skin treatment. The coupling foil p comprised of atransparent foil, the transparent foil at one side being provided with atransparent mixture of a polar substance and an apolar substance.Preferably, the foil is more hydrophobic than the transparent materialfrom which the transparent exit window is made, which is typicallyplastics or glass. Such a coupling foil can be used together with theoptical skin treatment devices that are already known from the priorart. The main requirement for the optical skin treatment device is thatit has a suitable exit window, e.g. made of glass or plastics. Thecoupling foil may be a dispensable product which is applied to thedevice just before each skin treatment. For example, the coupling foilis a covering for pulling over at least the transparent exit window ofthe interface element of the device for light based skin treatment.

It is to be noted that the transparent foil and the transparent mixturemay be provided separately. Before applying the covering to theinterface element, the transparent mixture should then first be appliedto the transparent exit window and/or the surface of the covering thatis going to face the transparent exit window. In a similar way theviscous fluid, e.g. massage oil or another type of organic oil, to beapplied between the skin and the transparent foil may already be presenton the transparent foil surface or could be provided separately.

According to a further aspect of the invention, a system for light basedskin treatment is provided, the system comprising a device for lightbased skin treatment and a coupling foil. The device comprises a lightsource for providing an incident light beam for treating a skin. Thedevice further comprises optical elements for focusing the incidentlight beam in a focal point inside the skin. The device furthercomprises a skin interface element for, during use of the device,providing optical coupling of the incident light beam from the deviceinto the skin, the skin interface element comprising a transparent exitwindow for allowing the incident light beam to leave the device. Thecoupling foil comprises a transparent foil, wherein the transparentfoil, at one side, is provided with a transparent mixture of a polarsubstance and an apolar substance. The transparent foil is morehydrophobic than the transparent exit window of the device.

According to a further aspect of the invention, a method for opticallycoupling of an incident light beam from a device for light based skintreatment into a skin is provided, the method comprising applying afluid having a viscosity of about 20 to about 80 mPa·s. to the skin,applying a transparent foil to the skin provided with the fluid,applying a transparent mixture of a polar substance and an apolarsubstance to a side of the transparent foil facing away from the skin,and pressing a transparent exit window of a skin interface element ofthe device to the transparent foil provided with the transparentmixture, the transparent foil being more hydrophobic than thetransparent exit window.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 schematically shows a skin treatment device according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically shows a skin treatment device 10 according to theinvention. The device 10 comprises a light source 18 for providing anincident light beam 21 for treating human or animal skin 30. Theincident light beam 21 is typically a pulsed laser. For example, Nd:YAGlasers with emission at 1064 μm (micrometer) are used for laser inducedoptical breakdown (LIOB) skin treatment. Optical elements are providedfor focusing the pulsed laser beam 21 inside the skin 30. Part or all ofthe optical elements may be provided in an interface element 11 which,during use of the device 10, is pressed onto or makes contact with theskin 30 to be treated.

The skin 30 comprises multiple layers with different optical properties.The epidermis 16 is composed of the outermost layers and forms awaterproof protective barrier. The outermost layer of the epidermis isthe stratum corneum which, due to its microscopic fluctuations inroughness, impedes the coupling of light between the device 10 and theskin 30. Underneath the epidermis 16, the dermis 17 is situated. Thedermis 17 comprises the collagen fibers at which the skin treatment isaimed. The purpose of the skin treatment is to create a focus 22 of thepulsed laser beam 21 in the collagen of the dermis 17 in order to createmicroscopic lesions which result in new collagen formation.

In the figure, part of the interface element 11 as well as part of theskin 30 is enlarged in order to clarify its most important aspects. Theinterface comprises a regular transparent exit window 12 which istypically made of a relatively hydrophilic material, such as glass orplastics. For optimum optical coupling, the refractive index of thematerial of the exit window 12 is preferably close to that of theepidermis. For human skin, the refractive index typically is around 1.4.

According to the invention, some additional layers 13, 14, 15 areprovided in between the exit window 12 and the skin 30. Directly on theouter surface of the exit window 12, a transparent mixture 13 of a polarand an apolar substance is provided. The mixture 13 may be a gel orliquid which, due to its particular composition, adheres well to theexit window 12 above and the foil 14 underneath. This assures that thefoil 14 will remain flat and the coupling of the light 21 into the skin30 is optimal. As a suitable example, the mixture 13 may comprisepolypropylene glycol (PPG) and polyethylene glycol (PEG). Thetransparent foil 14 may, e.g., be a thin polyethylene terephthalate(PET) foil. For optimal optical coupling between the device 10 and theskin 30, the transparent mixture 13 and the foil 14 should haverefractive indexes that lie between the refractive indexes of the skin30 and the exit window 12.

Before use of the device 10 some oil, preferably an organic oil, isapplied to the skin 30 to be treated. For optimum results, the amount ofoil 15 to be applied should be well controlled, for example in the orderof 10-50 μl (microliters). The hydrophobic nature of the foil 14 and theepidermis layer 16 of the skin 30, allows the drop of oil to beeffectively smeared throughout the microstructure variations of the skin30 surface, resulting in uniform optical coupling. Instead of oil, otherfluids with a suitable viscosity may be used.

The layers of the transparent mixture 13 and the foil 14 may be anintegrated part of the interface element 11 of the skin treatment device10. These layers 13, 14 and/or the complete interface element 11 may besubstitutable. The oil 15 is typically provided separately, but may beprovided from a refillable reservoir in the device 10.

The transparent foil 14 may be provided as a separate substitutablecovering. Also the transparent mixture 13 may be provided separately. Inthat event, before each use of the device 10, the user applies someamount of the mixture 13 to the exit window 12 of the interface element11 and covers it with a new covering. Of course, the mixture 13 and thecovering may also be substituted after being used twice, 5 or 10 times.The covering may be provided with the mixture 13 already applied to itsinner surface, which would make it unnecessary for the user to apply themixture 13 to the exit window 12 before applying the covering.Optionally, the outer surface of the covering is already provided withthe oil 15 and the oil 15 does not have to be provided separately.

Alternatively, the oil 15, the foil 14 and the mixture 13 are allprovided separately and applied to the skin one by one before the exitwindow 12 of the interface element 11 of a skin treatment device 10 ispressed to the foil 14 covered with the mixture 13. Or oil 15 and foil145 are applied to the skin 30 and the mixture is provided to the exitwindow 12.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. In the claims, any reference signsplaced between parentheses shall not be construed as limiting the claim.Use of the verb “comprise” and its conjugations does not exclude thepresence of elements or steps other than those stated in a claim. Thearticle “a” or “an” preceding an element does not exclude the presenceof a plurality of such elements. The invention may be implemented bymeans of hardware comprising several distinct elements, and by means ofa suitably programmed computer. In the device claim enumerating severalmeans, several of these means may be embodied by one and the same itemof hardware. The mere fact that certain measures are recited in mutuallydifferent dependent claims does not indicate that a combination of thesemeasures cannot be used to advantage.

The invention claimed is:
 1. A method for optical coupling of anincident light beam from a device for light based skin treatment into askin, the method comprising: applying a fluid to the skin to be treated,applying a transparent foil to the portion of the skin provided with theapplied fluid as a separate replaceable covering arranged and configuredto be pulled over at least a transparent exit window, applying atransparent mixture of a polar substance and an apolar substance to aside of the transparent foil facing away from the skin, and pressing thetransparent exit window to the side of the transparent foil providedwith the transparent mixture, the transparent exit window adapted toallow the incident light beam to leave the device, and pulling thetransparent foil over the transparent exit window.
 2. The methodaccording to claim 1, wherein the fluid has a viscosity of 20 to 80mPa·s.
 3. The method according to claim 1, wherein the fluid has aviscosity of 20 mPa·s.
 4. The method according to claim 1, wherein thefluid is an organic oil.
 5. The method according to claim 1, wherein thetransparent foil is more hydrophobic than a material from which thetransparent exit window is made.
 6. The method according to claim 1,wherein the transparent mixture has a refractive index which lies inbetween a refractive index of the transparent foil and a refractiveindex of the transparent exit window.
 7. A method for optical couplingof an incident light beam from a device for light based skin treatmentinto a skin, the method comprising: applying a fluid to the skin to betreated, pressing a substitutable multi-layered integrated interfaceelement onto the portion of the skin covered with the applied fluid, themulti-layered integrated interface element comprising: a first layer,closest to the skin, consisting of a transparent foil, a second fluidlayer comprising a transparent mixture of a polar and an apolarsubstance, a third layer comprising a transparent exit window, such thatthe transparent mixture is applied directly to an outer surface of thetransparent exit window facing the skin thereby adhering the transparentexit window to the transparent foil, wherein the transparent foil ismore hydrophobic than the transparent exit window.
 8. The methodaccording to claim 7, wherein the fluid has a viscosity of 20 to 80mPa·s.
 9. The method according to claim 7, wherein the fluid has aviscosity of 20 mPa·s.
 10. The method according to claim 7, wherein thefluid is an organic oil.
 11. The method according to claim 7, whereinthe transparent mixture has a refractive index which lies in between arefractive index of the transparent foil and a refractive index of thetransparent exit window.
 12. A method for optical coupling of anincident light beam from a device for light based skin treatment into askin, the method comprising: applying a transparent mixture of a polarsubstance and an apolar substance to an inner surface of a transparentfoil not facing the skin, applying a fluid to an outer surface of thetransparent foil facing the skin, applying the transparent foil as aseparate replaceable covering arranged and configured to be pulled overat least a transparent exit window, pressing said transparent exitwindow to the transparent foil covering thereby adhering the transparentexit window to the transparent foil, wherein the transparent foil ismore hydrophobic than the transparent exit window.
 13. The methodaccording to claim 12, wherein the fluid has a viscosity of 20 mPa·s.14. The method according to claim 12, wherein the fluid is an organicoil.
 15. The method according to claim 12, wherein the transparentmixture has a refractive index which lies in between a refractive indexof the transparent foil and a refractive index of the transparent exitwindow.